1. Field of the Invention
This invention relates to a circuit for use in a video tape recorder or the like, and more particularly to a video signal processing circuit for reproducing an FM video signal.
2. Description of the Related Art
In a video tape recorder (hereinafter abbreviated to as VTR), an FM luminance signal and a low-pass filtered chroma signal are recorded on magnetic tape. As shown in FIG. 1, in the FM converted luminance signal (Y), the syncchip carrier and the white peak have frequencies of 3.4 MHz and 4.4 MHz, respectively. The frequency of the low-pass filtered chroma signal (C) is 625 KHz. Thus, the FM luminance signal and the low-pass filtered chroma signal have different frequency bands. In general, filters are used to separate and extract the above-mentioned signal components from the video signal obtained by playing back the magnetic tape. More specifically, a low-pass filter (LPF) extracts a chroma signal component, and a high-pass filter (HPF) extracts a luminance signal component.
FIG. 2 is a circuit diagram showing the conventional video signal processing circuit for separating and extracting those signal components from the FM video reproduction signal. The signal reproduced by magnetic head 11 is amplified by preamplifier 12. The output of preamplifier 12 is supplied to LPF 13, in which a chroma signal (C) is extracted from the video reproduction signal. The output of preamplifier 12 is also supplied through FM-AGC (FM-automatic gain control) circuit 14 to HPF (high pass filter) 15. The output of HPF 15 is amplitude-limited to a predetermined degree by limiter 16, and the then supplied to demodulator 17, in which the luminance signal (Y) is extracted.
In the conventional video signal processing circuit, HPF 15 must be of high degree and sharpness (Q) to obtain sufficient separation characteristics. Since a filter circuit of high degree and sharpness requires a large number of elements and is therefore expensive, the cost of manufacturing the circuit is high. Moreover, a large phase shift may occur in such a filter circuit, and it is difficult to compensate for the phase shift. Further, when a filter circuit of a high sharpness is used as a HPF, since the low-pass component is removed from the FM signal, a high-pass component is excluded from the demodulated luminance signal, resulting in an image having poor frequency characteristics (low shade gradient).
On the other hand, when a filter circuit with a low degree and sharpness is used as HPF 15, a low-pass converted chroma signal component is regarded as a lower band wave of the FM signal, and included in a luminance signal component.